This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A069832 Prefixing, suffixing or inserting a 7 in the number anywhere gives a prime. 9
 1, 3, 9, 19, 27, 33, 39, 57, 87, 97, 159, 177, 187, 433, 487, 541, 603, 691, 717, 753, 757, 853, 949, 1257, 1471, 1707, 2277, 2367, 2617, 2953, 4317, 4507, 4623, 4779, 4797, 5773, 6481, 6757, 6777, 7017, 7351, 7417, 7471, 7479, 7747, 7797, 7813, 7977 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Giovanni Resta, Table of n, a(n) for n = 1..2399 (terms < 10^13, first 201 terms from Harvey P. Dale) MATHEMATICA psi7Q[n_]:=Module[{idn=IntegerDigits[n]}, And@@PrimeQ[FromDigits/@ Table[ Insert[ idn, 7, i], {i, Length[idn]+1}]]]; Select[Range[8000], psi7Q] (* Harvey P. Dale, Sep 18 2012 *) CROSSREFS Cf. A068674, A068679, A069833. Sequence in context: A056682 A032670 A068677 * A057257 A029464 A029479 Adjacent sequences:  A069829 A069830 A069831 * A069833 A069834 A069835 KEYWORD base,nonn AUTHOR Amarnath Murthy, Apr 14 2002 EXTENSIONS More terms from Vladeta Jovovic, Apr 16 2002 Offset changed to 1 by Giovanni Resta, Oct 14 2019 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 5 17:42 EST 2019. Contains 329768 sequences. (Running on oeis4.)